The testing and evaluation of complex radar systems require special testing techniques. These testing techniques must be capable of processing radar transmissions which are in the 1 GHZ to 10 GHZ frequency range and have 500 MHZ bandwidths. The high center frequency and bandwidth makes signal processing difficult. The center frequency problem can be solved with simple heterodyning of the higher frequency to a lower one. However, this does not solve the bandwidth problem but only makes it worse as the bandwidth to center frequency ratio increases.
In the case of radar target simulators where it is desired to delay the radar signals in fiber acoustic wave guides by one millisecond or more to account for a range delay, a reduction in the center frequency and bandwidth is of great interest. For example, a yttrium-iron-garnett (YIG) acoustic delay line crystal attenuates a 400 MHZ signal about 0.031 db per microsecond. A one millisecond delay for 400 MHZ would, therefore be 31 db and for 4000 MHZ, 3100 db which shows the importance of center frequency reduction. As stated above, reducing the center frequency without reducing bandwidth can cause the modulation index to become unreasonably large. Therefore, frequency division becomes of great interest since it keeps a constant modulation index.